To access your mailbox through webmail, do any of the following :
In a Web browser, visit the URL webmail.example.com, where example.com is the Internet address of your website. When prompted, specify your full email address as the username (for example, mail@example.com), and specify the email address password.
When logged in to Plesk, click the Mail tab, and in the list of email addresses, click an icon corresponding to the email address you need.